Display apparatus

ABSTRACT

A display apparatus comprises a spatial light modulator and optical elements in series therewith. The optical elements provide a first parallax element being a parallax barrier capable of directing light output from the display apparatus into a first plurality of viewing windows, and a second parallax element capable of directing light output from the display apparatus into a second plurality of viewing windows. In a first mode, the first and second parallax elements have substantially no directional effect on the light output from the display apparatus. In a second mode, the first parallax element directs light output from the display apparatus into the first plurality of viewing windows and the second optical element has substantially no directional effect. In a third mode, the second optical element directs light output from the display apparatus into the second plurality of viewing windows and the first parallax element has substantially no directional effect.

FIELD OF THE INVENTION

The present invention relates to display apparatuses for displaying animage. Such an apparatus may be used in a switchable two dimensional(2D)/three dimensional (3D) autostereoscopic display apparatus; for aswitchable high brightness reflective display system; for a multi-userdisplay system; or for a directional lighting system. Such systems maybe used in computer monitors, telecommunications handsets, digitalcameras, laptop and desktop computers, games apparatuses, automotive andother mobile display applications.

DESCRIPTION OF RELATED ART

3D Displays

Normal human vision is stereoscopic, that is each eye sees a slightlydifferent image of the world. The brain fuses the two images (referredto as the stereo pair) to give the sensation of depth. Three dimensionalstereoscopic displays replay a separate, generally planar, image to eachof the eyes corresponding to that which would be seen if viewing a realworld scene. The brain again fuses the stereo pair to give theappearance of depth in the image.

FIG. 1 a shows in plan view a display surface in a display plane 1. Aright eye 2 views a right eye homologous image point 3 on the displayplane and a left eye 4 views a left eye homologous point 5 on thedisplay plane to produce an apparent image point 6 perceived by the userbehind the screen plane.

FIG. 1 b shows in plan view a display surface in a display plane 1. Aright eye 2 views a right eye homologous image point 7 on the displayplane and a left eye 4 views a left eye homologous point 8 on thedisplay plane to produce an apparent image point 9 in front of thescreen plane.

FIG. 1 c shows the appearance of the left eye image 10 and right eyeimage 11. The homologous point 5 in the left eye image 10 is positionedon a reference line 12. The corresponding homologous point 3 in theright eye image 11 is at a different relative position 3 with respect tothe reference line 12. The separation 13 of the point 3 from thereference line 12 is called the disparity and in this case is a positivedisparity for points which will lie behind the screen plane.

For a generalised point in the scene there is a corresponding point ineach image of the stereo pair as shown in FIG. 1 a. These points aretermed the homologous points. The relative separation of the homologouspoints between the two images is termed the disparity; points with zerodisparity correspond to points at the depth plane of the display. FIG. 1b shows that points with uncrossed disparity appear behind the displayand FIG. 1 c shows that points with crossed disparity appear in front ofthe display. The magnitude of the separation of the homologous points,the distance to the observer, and the observer's interocular separationgives the amount of depth perceived on the display.

Stereoscopic type displays are well known in the prior art and refer todisplays in which some kind of viewing aid is worn by the user tosubstantially separate the views sent to the left and right eyes. Forexample, the viewing aid may be colour filters in which the images arecolour coded (e.g. red and green); polarising glasses in which theimages are encoded in orthogonal polarisation states; or shutter glassesin which the views are encoded as a temporal sequence of images insynchronisation with the opening of the shutters of the glasses.

Autostereoscopic displays operate without viewing aids worn by theobserver. In autostereoscopic displays, each of the views can be seenfrom a limited region in space as illustrated in FIG. 2. A parallaxelement is used, being an element capable of directing light into aplurality of viewing windows. The parallax element may be, for example,a parallax barrier or an array of lenses such as formed by a lenticularscreen.

FIG. 2 a shows a display apparatus 16 with an attached parallax opticalelement 17. The display apparatus 16 produces a right eye image 18 forthe right eye channel. The parallax optical element 17 directs light ina direction shown by the arrow 19 to produce a right eye viewing window20 in the region in front of the display. An observer places their righteye 22 at the position of the window 20. The position of the left eyeviewing window 24 is shown for reference. The viewing window 20 may alsobe referred to as a vertically extended optical pupil.

FIG. 2 b shows the left eye optical system. The display apparatus 16produces a left eye image 26 for the left eye channel. The parallaxoptical element 17 directs light in a direction shown by the arrow 28 toproduce a left eye viewing window 30 in the region in front of thedisplay. An observer places their left eye 32 at the position of thewindow 30. The position of the right eye viewing window 20 is shown forreference.

The system comprises a display and an optical steering mechanism. Thelight from the left image 26 is sent to a limited region in front of thedisplay, referred to as the viewing window 30. If an eye 32 is placed atthe position of the viewing window 30 then the observer sees theappropriate image 26 across the whole of the display 16. Similarly theoptical system sends the light intended for the right image 18 to aseparate window 20. If the observer places their right eye 22 in thatwindow then the right eye image will be seen across the whole of thedisplay. Generally, the light from either image may be considered tohave been optically steered (i.e. directed) into a respectivedirectional distribution.

FIG. 3 shows in plan view a display apparatus 16,17 in a display plane34 producing the left eye viewing windows 36, 37, 38 and right eyeviewing windows 39,40,41 in the window plane 42. The separation of thewindow plane from the display is termed the nominal viewing distance 43.The windows 37,40 in the central position with respect to the displayare in the zeroth lobe 44. Windows 36, 39 to the right of the zerothlobe 44 are in the +1 lobe 46, while windows 38,41 to the left of thezeroth lobe are in the −1 lobe 48.

The viewing window plane of the display represents the distance from thedisplay at which the lateral viewing freedom is greatest. For pointsaway from the window plane, there is a diamond shaped autostereoscopicviewing zone, as illustrated in plan view in FIG. 3. As can be seen, thelight from each of the points across the display is beamed in a cone offinite width to the viewing windows. The width of the cone may bedefined as the angular width.

If an eye is placed in each of a pair viewing zones such as 37,40 thenan autostereoscopic image will be seen across the whole area of thedisplay. To a first order, the longitudinal viewing freedom of thedisplay is determined by the length of these viewing zones.

The variation in intensity 50 across the window plane of a display(constituting one tangible form of a directional distribution of thelight) is shown with respect to position 51 for idealised windows inFIG. 4 a. The right eye window position intensity distribution 52corresponds to the window 41 in FIG. 3, and intensity distribution 53corresponds to the window 37, intensity distribution 54 corresponds tothe window 40 and intensity distribution 55 corresponds to the window36.

FIG. 4 b shows the intensity distribution with position schematicallyfor more realistic windows. The right eye window position intensitydistribution 56 corresponds to the window 41 in FIG. 3, and intensitydistribution 57 corresponds to the window 37, intensity distribution 58corresponds to the window 40 and intensity distribution 59 correspondsto the window 36.

The quality of the separation of images and the extent of the lateraland longitudinal viewing freedom of the display is determined by thewindow quality, as illustrated in FIG. 4. FIG. 4 a shows the idealviewing windows while FIG. 4 b is a schematic of the actual viewingwindows that may be outputted from the display. Several artefacts canoccur due to inadequate window performance. Cross talk occurs when lightfrom the right eye image is seen by the left eye and vice versa. This isa significant 3D image degradation mechanism which can lead to visualstrain for the user. Additionally, poor window quality will lead to areduction in the viewing freedom of the observer. The optical system isdesigned to optimised the performance of the viewing windows.

Parallax Barrier Displays

One type of well known flat panel autostereoscopic display comprises abacklight, an array of electronically adjustable pixels (known as aSpatial Light Modulator, SLM) arranged in columns and rows and aparallax barrier attached to the front of the display as illustrated inplan view in FIG. 5.

A backlight 60 produces a light output 62 which is incident on an LCDinput polariser 64. The light is transmitted through a TFT LCD substrate66 and is incident on a repeating array of pixels arranged in columnsand rows in an LCD pixel plane 67. The red pixels 68,71,74, green pixels69,72,75 and blue pixels 70,73 each comprise an individuallycontrollable liquid crystal layer and are separated by regions of anopaque mask called a black mask 76. Each pixel comprises a transmissiveregion, or pixel aperture 78. Light passing through the pixel ismodulated in phase by the liquid crystal material in the LCD pixel plane67 and in colour by a colour filter positioned on an LCD colour filtersubstrate 80. The light then passes through an output polariser 82 afterwhich is placed a parallax barrier 84 and a parallax barrier substrate86. The parallax barrier 84 comprises an array of vertically extendedtransmissive regions 92 separated by vertically extended opaque regions93 and serves to direct light from alternate pixel columns 69,71,73,75to the right eye as shown by the ray 88 for light from pixel 69 and fromthe intermediate columns 68,70,72,74 to the left eye as shown by the ray90 (this overall light direction pattern forming another example of adirectional distribution of light). The observer sees the light from theunderlying pixel illuminating the aperture of the barrier, region 92.

In this document, an SLM includes both ‘light valve’ devices such asliquid crystal displays and emissive devices such as electroluminescentdisplays and LED displays.

The pixels of the display are arranged as rows and columns separated bygaps, (generally defined by the black mask 76 in a liquid crystaldisplay, LCD) with the parallax barrier being an array of verticallyextended slit regions 92 of pitch close to twice the pitch of the pixelcolumns. The parallax barrier limits the range of angles from whichlight from each pixel column can be seen, thus creating the viewingwindows at a region in front of the display. The angles of the outputcone from the display are determined by the width and shape of the pixelaperture and the alignment and aberrations of the parallax barrier.

In order to steer the light from each pixel to the viewing window, thepitch of the parallax barrier is slightly smaller than twice the pitchof the pixel array. This condition is known as ‘viewpoint correction’.In such a display, the resolution of each of the stereo pair images ishalf the horizontal resolution of the base LCD, and two views arecreated.

Thus, the light from the odd columns of pixels 68,70,72,74 can be seenfrom the left viewing window, and the light from the even columns ofpixels 69,71,73,75 can be seen from the right viewing window. If theleft eye image data is placed on the odd columns of the display and theright eye image data on the even columns then the observer in thecorrect ‘orthoscopic’ position should fuse the two images to see anautostereoscopic 3D image across the whole of the display.

There will be light leakage between the two views such that some of theleft eye view will be seen by the right eye and vice versa. This leakageis termed image cross-talk. Cross talk is an important mechanism forgenerating visual strain when viewing 3D displays, and its control is amajor driver in 3D display development. For flat panel autostereoscopicdisplays (in particular those based on LCD technology), the limitationto window performance is generally determined by the shape and apertureratio of the pixel and the quality of the optical element.

In a parallax barrier type display, the columns directly under the slitsare imaged to a first pair of windows in the zeroth lobe of the display.The adjacent pixel columns are also imaged to viewing windows, in +1 and−1 lobes of the display. Thus as can be seen in FIG. 3, if the usermoves laterally outside the orthoscopic zone then light from theincorrect image will be sent to each eye. When the right eye sees theleft eye view and vice versa, the image is termed ‘pseudoscopic’,compared to the correct orthoscopic condition.

In order to increase the lateral viewing freedom of the display, morethan two pixel columns can be placed under each slit of the barrier. Forexample, four columns will create four windows in which the view ischanged for each window. Such a display will give a ‘look-around’appearance as the observer moves. The longitudinal freedom is alsoincreased by such a method. However, in this case, the resolution of thedisplay is limited to one quarter of the resolution of the base panel.

Parallax barriers rely on blocking the light from regions of the displayand therefore reduce the brightness and device efficiency, generally toapproximately 20-40% of the original display brightness.

Parallax barriers are not readily removed and replaced due to therequirements of sub-pixel alignment tolerances of the barrier withrespect to the pixel structure of the display in order to optimise theviewing freedom of the display. The 2D mode is half resolution.

Parallax Barrier Optical Components

One type of parallax barrier display in which the parallax barrierelements are placed in front of the display device is disclosed in T.Okoshi “Three Dimensional Imaging Techniques”, Academic Press 1976.

In another type of a parallax barrier display, the parallax elements maybe embodied as slits behind the display, as disclosed in G. Hamagishi etal “A Display System with 2D/3D compatibility”, Proc. SID 1998 pp915-918. It can be shown that such a display suffers from Fresneldiffraction artefacts, limiting the quality of the viewing windows thatcan be obtained.

In another type of a parallax barrier display, the parallax elements maybe embodied as light lines interspersed by dark regions as disclosed inU.S. Pat. No. 4,717,949. It can be shown that such a display suffersfrom Fresnel diffraction artefacts, limiting the quality of the viewingwindows that can be obtained, G. Woodgate et al Proc. SPIE Vol. 3957“Flat panel autostereoscopic displays—characterisation and enhancement”pp 153-164, 2000.

Lenticular Displays

Another type of parallax optic (cf. parallax barriers) well known in theart for use in stereoscopic displays is called the lenticular screen,which is an array of vertically extended cylindrical microlenses. Theterm “cylindrical” as used herein has its normal meaning in the art andincludes not only strictly spherical lens shapes but also asphericallens shapes. The pitch of the lenses again corresponds to the viewpointcorrection condition. The curvature of the lenses is set substantiallyso as to produce an image of the LCD pixels at the window plane. As thelenses collect the light in a cone from the pixel and distribute it tothe windows, lenticular displays have the full brightness of the basepanel.

FIG. 6 shows the structure of a prior art lenticular display apparatus.The apparatus is configured as described in FIG. 5 up to the outputpolariser 82. The light then passes through a lenticular screensubstrate 94 and a lenticular screen 96 which is formed on the surfaceof the lenticular screen substrate 94. As for the parallax barrier, thelenticular screen 96 serves to direct light from alternate pixel columns69,71,73,75 to the right eye as shown by the ray 88 from the pixel 69and from the intermediate columns 68,70,72,74 to the left eye as shownby the ray 90 from pixel 68. The observer sees the light from theunderlying pixel illuminating the aperture of the individual lenticule,98 of the lenticular screen 96. The extent of the captured light cone isshown by the captured rays 100.

Lenticular displays are described in T. Okoshi “Three DimensionalImaging Techniques”, Academic Press, 1976. One type of lenticulardisplay using a spatial light modulator is described in U.S. Pat. No.4,959,641. The invention of '641 describes non-switching lenticularelements in air.

Such a display may suffer from undesirable visibility of the lenssurface due to reflections and scatter at and near to the lenses 96which will degrade the contrast of the image. Reflections could be forexample due to Fresnel reflections.

Extended Viewing Freedom

The viewing freedom of the flat panel displays described above islimited by the window structure of the display.

A display in which the viewing freedom is enhanced by measuring theposition of an observer and moving the parallax element incorrespondence is described in EP0 829 743. Such an observer measurementapparatus and mechanical actuation is expensive and complex.

A display in which the window optical structure is not varied (a fixedparallax optic display for example) and the image data is switched incorrespondence to the measured position of the observer such that theobserver maintains a substantially orthoscopic image is described forexample in EP0721131.

A lenticular display using cylindrical lenses that are tilted withrespect to columns of pixels of a display is described in “Multiview3D—LCD” published in SPIE Proceedings Vol. 2653, 1996, pages 32 to 39.

2D-3D Switchable Displays

As described above, the use of parallax optics to generate a spatiallymultiplexed 3D display limits the resolution of each image to at besthalf of the full display resolution. In many applications, the displayis intended to be used for a fraction of the time in the 3D mode, and isrequired to have a full resolution artefact free 2D mode.

One type of display in which the effect of the parallax optic is removedis Proc. SPIE vol. 1915 Stereoscopic Displays and Applications IV (1993)pp 177-186, “Developments in Autostereoscopic Technology at DimensionTechnologies Inc.”, 1993. In this case, a switchable diffuser element isplaced in the optical system used to form the light lines. Such aswitchable diffuser could be for example of the Polymer Dispersed LiquidCrystal type in which the molecular arrangement switches between ascattering and non-scattering mode on the application of an appliedvoltage across the material. In the 3D mode, the diffuser is clear andlight lines are produced to create the rear parallax barrier effect. Inthe 2D mode, the diffuser is scattering and the light lines are washedout, creating the effect of a uniform light source. In this way, theoutput of the display is substantially Lambertian and the windows arewashed out. An observer will then see the display as a full resolution2D display. Such a display suffers from Fresnel diffraction artefacts inthe 3D mode, as well as from unwanted residual scatter in the diffuser'sclear state which will increase the display cross-talk. Therefore, sucha display is likely to exhibit higher levels of visual strain.

In another type of switchable 2D-3D display [for example EP0 833 183], asecond LCD is placed in front of the display to serve as a parallaxoptic. In a first mode, the parallax LCD is clear so that no windows areproduced and an image is seen in 2D. In a second mode, the apparatus isswitched so as to produce slits of a parallax barrier. Output windowsare then created and the image appears to be 3D. Such a display hasincreased cost and complexity due to the use of two LCD elements as wellas being of reduced brightness or having increased power consumption. Ifused in a reflective mode 3D display system, parallax barriers result invery poor brightness due to attenuation of light by the blocking regionsof the parallax barrier both on the way in and out of the display.

In another type of switchable 2D-3D display [EP 0 829 744] a parallaxbarrier comprises a patterned array of half wave retarder elements. Thepattern of retarder elements corresponds to the pattern of barrier slitsand absorbing regions in a parallax barrier element. In a 3D mode ofoperation, a polariser is added to the display so as to analyse theslits of the patterned retarder. In this way, an absorbing parallaxbarrier is produced. In the 2D mode of operation, the polariser iscompletely removed as there is no involvement of any polarisationcharacteristics in the 2D mode of operation. Thus the output of thedisplay is full resolution and full brightness. One disadvantage is thatsuch a display uses parallax barrier technology and thus is limited toperhaps 20-30% brightness in the 3D mode of operation. Also, the displaywill have a viewing freedom and cross talk which is limited by thediffraction from the apertures of the barrier.

It is known to provide electrically switchable birefringent lenses forpurposes of switching light directionally. It is known to use suchlenses to switch a display between a 2D mode of operation and a 3D modeof operation.

For example, electrically switchable birefringent liquid crystalmicrolenses are described in European Optical Society Topical MeetingsDigest Series: 13, 15-16 May 1997 L. G. Commander et al “Electrodedesigns for tuneable microlenses” pp 48-58.

In another type of switchable 2D-3D display [U.S. Pat. No. 6,069,650, WO98/21620], switchable microlenses comprising a lenticular screen filledwith-liquid crystal material are used to change the optical power of alenticular screen. [U.S. Pat. No. 6,069,650, WO 98/21620] teaches theuse of an electro-optic material in a lenticular screen whose refractiveindex is switchable by selective application of an electric potentialbetween a first value whereby the light output directing action of thelenticular means is provided and a second value whereby the light outputdirecting action is removed.

A 3D display comprising a liquid crystal Fresnel lens is described in S.Suyama et al “3D Display System with Dual Frequency Liquid CrystalVarifocal Lens”, SID 97 DIGEST pp 273-276.

In another type of switchable 2D-3D display, as described inPCT/GB2002/003513 a passive birefringent microlens is switched between a2D and 3D mode by means of controlling the polarisation of light whichpasses through the lens and reaches an observer. It is also known fromthis reference to use twist in passive birefringent lenses in order torotate the input polarisation such that the birefringent microlensgeometric axis is parallel to the birefringent material axis at the lenssurface.

It is known to provide polarised output from organic electroluminescentdisplay. “Polarized Electroluminescence from an Anisotropic NematicNetwork on a Non-contact Photoaligninent Layer”, A. E. A. Contoret, S.R. Farrar, P. O. Jackson, S. M. Khan, L. May, M. O'Neill, J. E.Nicholls, S. M. Kelly and G. J. Richards, Adv. Mater. 2000, 12, No. 13,July 5 p 971 describes a polarised electroluminescent display apparatusand demonstrates that polarisation efficiencies of 11:1 can be achievedin practical systems.

Polarisation Activated Microlenses

One prior art system which enables switching of a microlens function bycontrolling the polarisation of light passing through the lens isdescribed in WO-03/015424 and is shown in plan view in FIG. 7 andincorporated herein by reference.

A backlight 102 produces illumination 104 of an LCD input polariser 106.The light passes through a thin film transistor (TFT) substrate 108 andis incident on a pixel layer 110 comprising individually controllablephase modulating pixels 112-126. The pixels are arranged in rows andcolumns and comprise a pixel aperture 128 and may have a separatingblack mask 130. The light then passes through an LCD counter substrate132 and a lens carrier substrate 136 upon which is formed a birefringentmicrolens array 138. The birefringent microlens array 138 comprises anisotropic lens microstructure 140 and an aligned birefringent materialwith an optical axis direction 142. The output of the birefringent lensthen passes through a lens substrate 144 and a polarisation modifyingdevice 146.

Each birefringent lens of the lens array is cylindrical; the lens array138 is a lenticular screen and the geometrical axis of the lenses is outof the page. The pitch of the lenses in this example is arranged to besubstantially twice the pitch of the pixels of the display such that atwo view autostereoscopic display is produced.

In a first mode of operation, the polarisation modifying device 146 isconfigured to transmit light with a polarisation state which is parallelto the ordinary axis of the birefringent material of the microlensarray. The ordinary refractive index of the material (such as a liquidcrystal material) is substantially matched to the index of the isotropicmicrostructure 140. Thus the lenses have no optical effect and there issubstantially no change to the directional distribution of the output ofthe display. In this mode, an observer will see all the pixels 112-126of the display with each eye, and a 2D image will be produced.

In a second mode of operation, the polarisation modifying device 146 isconfigured to transmit light with a polarisation state which is parallelto the extraordinary axis of the birefringent microlens array. Theextraordinary refractive index of the material (such as a liquid crystalmaterial) is different to the index of the isotropic microstructure 140.Thus the lenses have an optical effect and there is a change to thedirectional distribution of the output of the display. This directionaldistribution can be set as well known in the art so as an observercorrectly positioned at the front of the display will see a left imagein their left eye corresponding to light from left image pixels112,116,120,124 and in their right eye will see a right imagecorresponding to right image pixels 114,118,122,126. In this way, aswitchable 2D to 3D autostereoscopic display can be produced.

Lens arrays are particularly suitable for autostereoscopic displaysbecause they combine the properties of high optical efficiency, smallspot size and ability to be manufactured using well known lithographicprocessing techniques.

It is known to provide electrically switchable birefringent lenses forpurposes of switching light directionally. It is known to use suchlenses to switch a display between a 2D mode of operation and a 3D modeof operation.

FIG. 8 shows another example of the polarisation activated microlensesdisclosed in WO-2004/070451. In FIG. 8, the backlight and inputpolarisers are not shown. The polariser 146 of FIG. 7 is replaced by anelectrically controlled polarisation switch comprising additional ITOlayers 158 and 158 sandwiching a liquid crystal layer 160, an outputsubstrate 164 and an output polariser 166. An electrical signalcontroller 162 allows switching of the electric field between the ITOelectrodes to allow the liquid crystal material 160 to switch. Thisallows control of the polarisation state transmitted through the outputpolariser 166, and thus the function of the lens, as describedpreviously.

FIG. 9 shows a similar apparatus to that in FIG. 8, but an outputpolariser 154 is placed on the counter substrate 132, and the ITOelectrodes and LC layer 158,160 are placed between the lens 142 and thepolariser 154. Such a configuration allows switching of the lens withfull image contrast and brightness.

In the known switchable display apparatuses described above, thedirectional distribution of the output light is switachable between twomodes, typically one mode in which the directional distribution is notmodified such as a 2D mode and another mode in which the light outputfrom the display apparatus is directed into a plurality of viewingwindows such as a 3D mode. However it may be desirable to have furthermodes in which the light output from the display apparatus is directedinto a different plurality of viewing windows, for example to provideviewing windows when the display apparatus is used in two perpendicularorientations ie landscape and portrait. In practice, it is difficult toarrange a switchable display apparatus to achieve this.

In the known switchable display apparatuses described above, in the modein which the directional distribution of the light is modified themodification occurs in one dimension only, for example by directinglight into windows which extend linearly. This occurs due to the use oflinear parallax elements such as cylindrical lenses. As a result thedesired effect such as providing an autostereoscopic image only occursin one orientation of the display apparatus. However, displayapparatuses are often used in perpendicular orientations for example toallow the display of images both with landscape and portrait aspectratios, so it would be desirable to provide for modification of thedirectional distribution of the output light in two orthogonaldirections. It is difficult to arrange a switchable display apparatus toachieve this.

BRIEF SUMMARY OF THE INVENTION

According to the first aspect of the present invention, there isprovided a display apparatus comprising:

a spatial light modulator;

optical elements in series with the spatial light modulator and beingswitchable to provide:

a first parallax element being a parallax barrier capable of directinglight output from the display apparatus into a first plurality ofviewing windows; and

a second parallax element capable of directing light output from thedisplay apparatus into a second plurality of viewing windows,

the optical elements being switchable to operate in a first mode inwhich the first and second parallax elements have substantially nodirectional effect on the light output from the display apparatus, asecond mode in which the first parallax element directs light outputfrom the display apparatus into the first plurality of viewing windowsand the second optical element has substantially no directional effecton the light output from the display apparatus and a third mode in whichthe first parallax element has substantially no directional effect onthe light output from the display apparatus and the second opticalelement directs light output from the display apparatus into the secondplurality of viewing windows.

Thus the display apparatus is capable of switching between modes inwhich the light is directed into a first or a second plurality ofviewing windows. For example the viewing windows may extend orthogonallyto one another to provide viewing windows when the display apparatus isused in two perpendicular orientations ie landscape and portrait.

It is generally desirable in addition to switch the directionalfunctionality between a first non-directional mode in which thebehaviour of the display apparatus is substantially the same as the basepanel, and a second directional mode in which the behaviour of thedisplay apparatus is a directional display, for example anautostereoscopic display.

Prior art directional displays such as those incorporating cylindricallenses, arrays of elongate slits or rows of holograms produce parallaxin a single direction only. This conveniently serves to reduce the lossof resolution imposed by the optical element in the directional mode.However, the display orientation of the directional mode is fixed by thedirection of the optical element geometric axis, so the display can beused in one of landscape or portrait mode.

In devices such as mobile phones and cameras, it is desirable to rotatethe display to suite the image, for example between portrait andlandscape for a photo viewing application. Such functions cannot beenabled in a standard directional display.

Such a display apparatus exhibits resolution loss associated with eitherfirst or second directional distributions, but advantageously not withboth directional distributions. Therefore, the resolution of the mode ineach of the directional distribution is optimised, and the imageappearance is improved.

In one advantageous type of display apparatus, the first and secondparallax elements are formed separately and both arranged on the outputside of the spatial light modulator without any polariser between thefirst and second parallax elements.

Thus, it is possible to produce a display apparatus which is in a firstmode a 2D display, in a second mode a lenticular screen 3D display, forexample, for landscape operation and a third mode a parallax barrier 3Dmode, for example, for portrait operation. For each mode of operation,the lens and parallax barrier elements are placed between a single pairof polarisers and co-operate, based on the polarisation stated passedbetween the lens and parallax barrier. Advantageously it is notnecessary to incorporate an additional polariser or multiple substratesbetween the lens and parallax barrier. This allows the apparatus to befabricated with a reduced number of substrates, reducing weight andcost. Advantageously, this also allows the separation of the barrierfrom the pixel plane to be reduced, which reduces the nominal viewingdistance of the display for a given window size. Advantageously, each ofthe modes of the embodiment may enable the use of an output polariser asthe final element in the stack. Such a polariser reduces the visibilityof frontal reflections from components in the display.

Advantageously, a polariser is not required to be attached, for exampleby means of lamination, between each of the parallax elements. Thismeans that the elements can be fabricated as an optical stack withoutthe need for additional surfaces on which to mount an intermediatepolariser. Thus, advantageously the number of substrates can be reduced,and the elements can be processed at elevated temperature prior toattachment of the polariser elements. This allows for further costreduction and integration of the structures. This also means thatmultiple elements could be made using a motherglass and divided, furtherreducing cost and complexity of manufacture, which would not generallybe possible if an intermediate polariser layer were required.

In another advantageous type of display apparatus, the spatial lightmodulator has arranged in series therewith:

an input polariser;

a birefringent lens comprising a layer of isotropic material and a layerof birefringent material having a lens surface therebetween shaped todirect light output from the display apparatus into a second pluralityof windows;

electrodes for applying an electric field across the layer ofbirefringent material and patterned to provide alternating,independently addressable slit regions and barrier regions arranged sothat light passing through the slit regions is directed into a firstplurality of windows;

a switchable polarisation rotation element for selectively rotating thepolarisation of light passing therethrough; and

an analyser polariser,

the display apparatus being switchable by control of the voltage appliedto the electrodes and of the switchable polarisation rotation element tooperate in a first mode in which the birefringent lens has substantiallyno directional effect on the light output from the display apparatus, asecond mode in which light is output from the apparatus through the slitregions but not the barrier regions into the first plurality of viewingwindows and the lens surface has substantially no directional effect onthe light output from the display apparatus and a third mode in whichthe lens surface directs light output from the display apparatus intothe second plurality of viewing windows across the entirety of the slitregions and barrier regions.

Such a display apparatus advantageously enables the operation of a lensarray in a first mode and a parallax barrier in the second mode.Parallax barriers have advantages for directional displays such asautostereoscopic displays, that they can be lithographically formed tohigh precision. Further, they can be used with staggered aperturefunctions, so as to reduce the visibility of resolution loss ofdisplays. Thus, it is convenient for an autostereoscopic display to beconfigured in a first mode with a lens array and in a second mode with abarrier array. Thus, in a first mode, optimum results can be achieved bymatching the pixel pattern to a lens array, while in a second mode thepixel pattern can be matched to a barrier array. This can allow theviewing distance for the two directional modes to be matched forexample, as they have a defined separation.

Therefore, the appropriate optical element for the appropriateorientation can be enabled. This can be used to enable optimumperformance. The barrier may preferably be used to image the pixels inthe portrait mode, while the lens may preferably be used to image thepixels in the landscape mode. Thus the portrait mode parallax elementshould be closer to the pixels than the landscape mode device in orderthat the viewing distance of the display in each mode is similar.Additionally, in a landscape mode parallax barrier, the gaps between theslits of the barrier may be more visible to the human eye compared tothe gap between the slits in the portrait mode. Lenses do not sufferfrom the same gap visibility problem, because there is a continuousintensity across the lens aperture. Therefore, it may be advantageous toset the parallax barrier to image the pixels in the portrait mode, andthus closer to the display pixel plane than the lenses.

Desirably different optical functions are achieved by positioningoptical elements at different distances from the pixel plane of adisplay. A lens array with power in two axes (i.e. a two dimensionallens array which is not a cylindrical lens array) positioned in a singleplane does not achieve this function. Surface relief lens arraysdisadvantageously have a common sag between first and second axes, andso non-square lenses have substantially common focal lengths in the twoaxes. Therefore, a two dimensional lens array does not adequately imagethe pixel plane for operation in two axes. Thus it is difficult for atwo dimensional lens array to demonstrate high quality in both landscapeand portrait modes of autostereoscopic operation for example.

Configurations in which the parallax barrier and lenticular screen arein nominally the same plane have advantages for landscape and portraitoperation in systems using RGB strip pixel patterns. In particular, thesize of the optical spot at the pixel plane may be different forlandscape and portrait operation. In landscape operation for a panel asshown for example in FIG. 11 d, the lens may be designed to produce atightly focussed spot, and thus high window quality. The barrier may bedesigned to produce a wide, but advantageously achromatic, spot whichcovers a red, green and blue colour sub-pixel. Thus, an autostereoscopicimage may be produced, each orientation of which is optimised.

In another advantageous type of display apparatus, the spatial lightmodulator is a transmissive spatial light modulator, and the firstparallax element is arranged on the input side of the spatial lightmodulator and the second parallax element is arranged on output side ofthe spatial light modulator.

It may be desirable to us a parallax barrier in two modes of operationin two modes, which may simplify construction. Such a configuration isparticularly advantageous, as the sizes of pixels tends to be differentin landscape and portrait configurations. Thus the barriers for the twoconfigurations can be set at the corresponding separations so that thefinal viewing distance is nominally the same for both portrait andlandscape modes. Such an apparatus makes efficient use of the light inthe 2D mode, but suffers from losses in the 3D mode. Such an apparatusdoes not require the use of separate polarisers or substrates betweeneach element and thus reduces device complexity and cost whileoptimising viewing distance of the display in each mode of operation.Alternatively, the nominal viewing distances may be set to be differentto optimise the usability of the display for each panel orientation.

According to a second aspect of the present invention, there is provideda switchable display apparatus comprising:

a spatial light modulator; and

a birefringent lens arranged in series with the spatial light modulatorand comprising a layer of birefringent material between two opposinglens surfaces, the lens surfaces each shaped as an array of cylindricallenses extending substantially orthogonally to each other,

the display apparatus being switchable between a first mode in which thebirefringent lens has substantially no optical effect on light outputfrom the display apparatus and a second mode in which the directionaldistribution of the light output from the display apparatus is modifiedby both of the opposing lens surfaces.

Thus, the display apparatus is switchable into a mode in which thedirectional distribution of the light output from the display apparatusis modified by both of the opposing lens surfaces which are each shapedas an array of cylindrical lenses extending substantially orthogonallyto each other. This means it is possible to provide an effect, such asdirecting light into into a plurality of viewing windows to provide anautostereoscopic display, in two orthogonal directions. This allows theuse of the display apparatus in two perpendicular orientations, forexample in landscape or portrait orientations. This is achieved in amanner which is straightforward to construct and manufacture in practicebecause of the formation of the a birefringent lens as a layer ofbirefringent material between two opposing lens surfaces.

Such an apparatus does not require two switching elements, and can beconveniently manufactured. Further, the optical power of the elements onfirst and second surfaces can be tuned independently to match theunderlying pixel structure. Thus such an apparatus can produce moreeffective autostereoscopic viewing windows at a lower cost compared forexample using a two dimensional lens array in a single plane.

In another form of the second aspect of the present invention, there isprovided a switchable multiple parallax optic display device comprising:

a first parallax element arranged in series with a second parallaxelement; and

a linear polarisation transmitting element,

where the second parallax element cooperates with the first parallaxelement such that:

in a first mode such that the directional distribution of output lightis substantially unmodified (a non-directional mode); and

in a second mode such that the directional distribution of output lightis modified by the first and second parallax elements.

In the following a “non-directional mode” is used to mean a modeconfigured to provide substantially no directional modification of theinput illumination of the parallax optic.

A display apparatus in accordance with the present invention can be usedfor:

an autostereoscopic display means which can conveniently provide amoving full colour 3D stereoscopic image which may be viewed by theunaided eye in a first mode of operation and a full resolution 2D imagein a second mode of operation;

a switchable high brightness transmissive, transflective and reflectivedisplay system which in a first mode may exhibit substantiallynon-directional brightness performance and in a second mode may exhibitsubstantially directional brightness performance; and/or

a multi-viewer display means which can conveniently provide one 2D image(which may be moving full colour) to one observer and at least a seconddifferent 2D image to at least a second observer in one mode ofoperation and a single full resolution 2D image seen by all observers ina second mode of operation.

Different features of the first aspect of the invention may tend toprovide the following advantages singly or in any combination:

multiple modes of operation of the directional display apparatus can bearranged with independent performance;

a non-directional mode can be configured;

display has substantially the full brightness of the base display;

use of standard materials and processing techniques;

low cost;

compatible with off-the shelf flat panel displays; and

high performance of display in directional modes.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 a shows the generation of apparent depth in a 3D display for anobject behind the screen plane;

FIG. 1 b shows the generation of apparent depth in a 3D display for anobject in front of the screen plane;

FIG. 1 c shows the position of the corresponding homologous points oneach image of a stereo pair of images;

FIG. 2 a shows schematically the formation of the right eye viewingwindow in front of an autostereoscopic 3D display;

FIG. 2 b shows schematically the formation of the left eye viewingwindow in front of an autostereoscopic 3D display;

FIG. 3 shows in plan view the generation of viewing zones from theoutput cones of a 3D display;

FIG. 4 a shows the ideal window profile for an autostereoscopic display;

FIG. 4 b shows a schematic of the output profile of viewing windows froman autostereoscopic 3D display;

FIG. 5 shows the structure of a parallax barrier display;

FIG. 6 shows the structure of a lenticular screen display;

FIG. 7 shows a prior art polarisation activated microlens display;

FIG. 8 shows a prior art polarisation activated microlens display;

FIG. 9 shows a prior art polarisation activated microlens display;

FIG. 10 shows an example of a switchable display with a singledirectional mode with vertical and horizontal directionality;

FIG. 11 a shows portrait pixels on a landscape mode panel in landscapeorientation;

FIG. 11 b shows portrait pixels on a landscape mode panel in portraitorientation;

FIG. 11 c shows portrait pixels on a portrait mode panel in portraitorientation;

FIG. 11 d shows portrait pixels on a portrait mode panel in landscapeorientation;

FIG. 12 shows the image of the eye spot at the pixel plane for anautostereoscopic display with square lenses;

FIG. 13 shows an embodiment of the invention in which a switchableparallax barrier is configured in series with a birefringent lenselement;

FIG. 14 shows the structure of a display apparatus comprising aswitchable parallax barrier and a passive lens array;

FIG. 15 shows the structure of a display apparatus comprising aswitchable parallax barrier and an active lens array;

FIG. 16 shows the structure of a display apparatus comprising aswitchable parallax barrier and an active lens array with a commonswitchable liquid crystal layer;

FIG. 17 shows the structure of a display apparatus comprising aswitchable parallax barrier and a passive lens array;

FIG. 18 shows the structure of a display in which a switchable parallaxbarrier is arranged between a display panel and an active lens array;

FIG. 19 shows the structure of a display in which a switchable parallaxbarrier is arranged between a display panel and a passive lens array;

FIG. 20 shows the structure of a display apparatus comprising a rearswitchable parallax barrier and a switchable front lenticular screen;

FIG. 21 shows the structure of a display apparatus comprising twoswitchable parallax barriers; and

FIG. 22 shows the structure of a display comprising a switchable activelens switchable between first and second directionality;

FIG. 23 shows the structure of a display comprising a passive lens arrayswitchable between first and second directionality;

FIG. 24 shows the use of alignment features to align the first andsecond substrates of the display;

FIG. 25 shows the positioning of the alignment artifacts of FIG. 24;

FIG. 26 shows the structure of a display apparatus using a solidbirefringent lens component;

FIG. 27 shows the structure of a display in which two solid birefringentlens components are used;

FIG. 28 shows the structure of a display incorporating a switchablepassive lens component and a switchable parallax barrier component;

FIG. 29 shows the structure of a further display incorporating aswitchable passive lens component and a switchable parallax barriercomponent;

FIG. 30 shows one alignment of parallax optical elements and eye spotswith respect to the image pixels; and

FIG. 31 shows the structure of a display apparatus comprising a rearswitchable parallax barrier and a switchable front lenticular screen.

DETAILED DESCRIPTION OF THE INVENTION

Some of the various embodiments employ common elements which, forbrevity, will be given common reference numerals and a descriptionthereof will not be repeated. Furthermore the description of theelements of each embodiment applies equally to the identical elements ofthe other embodiments and the elements having corresponding effects,mutatis mutandis. Also, the figures illustrating the embodiments whichare displays show only a portion of display, for clarity. In fact, theconstruction is repeated over the entire area of the display.

In this specification, the direction of the optical axis of thebirefringent material (the director direction, or the extraordinary axisdirection) will be referred to as the birefringent optical axis. Thisshould not be confused with the optical axis of the lenses which isdefined in the usual way by geometric optics.

A cylindrical lens describes a lens in which an edge (which has a radiusof curvature and may have other aspheric components) is swept in a firstlinear direction. The geometric microlens axis is defined as the linealong the centre of the lens in the first linear direction, i.e.parallel to the direction of sweep of the edge. In a 2D-3D type display,the geometric microlens axis is vertical, so that it is parallel or at aslight angle to the columns of pixels of the display. In a brightnessenhanced display as described herein, the geometric microlens axis ishorizontal so that it is parallel to the rows of the pixels of thedisplay.

The eye spot in an autostereoscopic display is the intensitydistribution produced at the pixel plane when the optical systemproduces an image of the observer's eye in that plane. The eye spot willmove with respect to the pixels as the observer moves with respect tothe display. The eye spot for cylindrical optics is generally extendedvertically, whereas has a finite aspect ratio for non-cylindricaloptics. The eye spot is generally round from a square or round aperturedlens. The eye spot from a lens is determined by the phase function ofthe lens structure, and is generally determined by the aperture size andshape in a parallax barrier.

Prior art directional displays such as those incorporating cylindricallenses, arrays of elongate slits or rows of holograms produce parallaxin a single direction only. This conveniently serves to reduce the lossof resolution imposed by the optical element in the directional mode.However, the display orientation of the directional mode is fixed by thedirection of the optical element geometric axis, so the display can beused in one of landscape or portrait mode.

In devices such as mobile phones and cameras, it is desirable to rotatethe display to suite the image, for example between portrait andlandscape for a photo viewing application. Such functions cannot beenabled in a standard directional display.

It is generally desirable in addition to switch the directionalfunctionality between a first non-directional mode in which thebehaviour of the panel is substantially the same as the base panel, anda second directional mode in which the behaviour of the panel is adirectional display, for example an autostereoscopic display.

International Application No. PCT/GB04/002984 discloses use of a firstand a second birefringent lens array. Such a system advantageouslyprovides high efficiency and optical quality in a directional displaywith at least two modes of operation. However, it may be desirable touse other forms of birefringent parallax arrays such as a parallaxbarrier in at least one of the modes of operation.

Parallax barriers are optically inefficient in at least one mode ofoperation, for example they may typically show 30% efficiency or less inthe 3D mode of operation. They may also show reduced optical quality inoperation in the 3D mode compared to a lens of a lenticular screen.However, parallax barriers advantageously are substantially planarstructures that can be fabricated using relatively standard liquidcrystal processing technology, not requiring the fabrication ofmicrostructures. Such elements may have reduced complexity and cost offabrication, as well as being thinner.

It may be desirable to produce a non-directional display in a first modeof operation, a lens array optical element mode in a second mode ofoperation and a parallax barrier optical element in a third mode ofoperation.

One apparatus which can be switched between a non-directional anddirectional mode and can allow directional operation in both portraitand landscape orientations is illustrated in FIG. 10 for the case of aPolarisation Activated Microlens display, similar to structure andoperation as that shown in FIG. 8. An LCD panel output substrate 200 hasa linear output polarisation 202. The output polarisation state isincident on a lens array comprising a birefringent material (not shown)sandwiched between a counter substrate 204 with an alignment direction206 and a surface relief lens 208 with an alignment direction 210. Theoutput light passes through a liquid crystal shutter comprising ITOelectrodes 212,214 with respective alignment directions 216,218sandwiching a liquid crystal layer (not shown). The light then passesthrough a final output polariser 220 with polarisation transmissiondirection 222.

The lens array 208 of such a display is non-cylindrical. The lens may bearranged to have the pitch of for example substantially two columns ofpixels in a first direction, and two rows of pixels in a seconddirection. Thus the display can in principle show an autostereoscopicdisplay in both landscape and portrait modes of operation. The panel canbe oriented in this example as a landscape panel with vertical columnsof red, green, and blue pixels for example. To switch between the twomodes, the left and right eye data on the panel can be in adjacentcolumns for landscape operation and adjacent rows for portraitoperation.

Disadvantageously, a surface relief lens will have a single maximumdepth which is the same for both horizontal and vertical lens axes.However, as the lens will generally be of non-square shape then theradius of curvature can be significantly different for horizontal andvertical directions. Thus, the focal length of the lens will bedifferent in the two orientations. However, the pixel plane is a singlefixed distance from the lens surface and so the apparatus can only befocussed for optimum operation in one orientation, or set at acompromise focus for both. This means that in at least one mode, thewindows produced may be undesirable quality. Additionally, in thedirectional mode of operation, the display will provide imaging of thegaps between pixels in both vertical and horizontal axes, so that as thedisplay is tilted about an axis, the image will appear to flicker.Additionally, the display will show limited resolution in bothhorizontal and vertical directions.

FIG. 11 clarifies the description of landscape and portrait panels. InFIG. 11 a, a landscape panel 300 has columns of red 302, green 304 andblue 306 pixels. When rotated to portrait mode as shown in FIG. 11 b,the pixel columns also rotate. FIG. 11 c shows a portrait panel 308 withcolumns of red 310, green 312 and blue 314 pixels. FIG. 11 d shows theportrait panel rotated for landscape use.

Alternatively, the lens 208 can comprise square lenses so that the sizeof the optical spot at the pixel plane is the same in vertical andhorizontal axes. The size of the optical spot can be set so as to coverthe width of an RGB triplet of pixels as shown in FIG. 12. The pixelcolumns of red 302, green 304 and blue 306 pixels are arranged in rows400, 402. In such a square lens system, the eye spot 404 is the image ofthe observer's eye at the pixel plane, and will thus be round as opposedto elongate, as found for cylindrical parallax elements. Thus,disadvantageously, the intensity distribution and colour of the imageseen in the window plane will vary as the observer moves laterally orvertically. Such a system will have similar optical performance in bothhorizontal and vertical directions of operation.

Further disadvantageously, it can be difficult to maintain highperformance alignment of the birefringent material at the surface of thelens array as a single alignment direction is required for thebirefringent material, but the surface normals of the lens vary in twodimensions.

Thus, a non-cylindrical lens can be used to switch between a directionaldisplay which can be used in both portrait and landscape orientation forexample, and non-directional display. However, such a display presents anumber of disadvantages including those stated above.

In the case of a time sequential panel, in which the colour filters areomitted and the backlight is switched in synchronization with colourdata, the pixels may be square profile rather than rectangular. In thiscase, the optical function in both directions may be the same. Such asystem means that the optical components can be optimised while lying inthe same plane. Therefore, such a display advantageously can producehigh image quality for both landscape and portrait modes, and may beformed in a single layer, thus reducing the cost of the system.

In the following diagrams, where a symbol is used to illustrate theorientation of the birefringent material at a surface, or in or out ofthe plane of the page, it is to be understood that the orientation maydeviate a small amount from that shown because of pre-tilt of thebirefringent material at the surface, as is well known in the art.

The spatial light modulator of the invention may be a transmissivedisplay, a reflective display, a transflective display or an emissivedisplay (such as an organic electroluminescent display) or acombination. In the case of non-polarised displays, an additionalpolariser and waveplate layers may be used.

FIG. 13 shows one embodiment of the invention in which a switchablebirefringent parallax barrier comprising a patterned electrodeaddressing substrate 300, alignment layers (not shown) and a switchablebirefringent layer 301 is configured in series with a birefringent lenselement comprising a structured polymer surface 302, alignment layers(not shown) and a birefringent layer 303, which may be switchable bymeans of an applied electric field for example. The elements are placedin front of a display device 304, and may be separated by a layer 306which may comprise additional alignment layers and electrodes (notshown). Alternatively, the lens 302, 303 may be placed between thedisplay device 304 and the birefringent barrier 300, 301.

An additional polarisation rotation element (not shown) which may be forexample a liquid crystal cell may also be incorporated in series withinthe structure to control the polarisation of light falling on or exitingthe lens component. Such a polarisation rotation element may have afunction of rotating an incident linear polarisation state through 90degrees and may be for example a twisted nematic structure, or otherswitchable waveplate structure.

The birefringent parallax barriers of this invention have the propertythat in at least one mode of operation they are capable, over at least aportion of their area, of rotating an incident linear polarisation statethrough an angle which may be 90 degrees. Such devices may be forexample a twisted nematic structure, or other switchable waveplatestructure. The polarisation rotation function may be patterned so thatthe regions corresponding to slits and barriers of a parallax barriermay have respectively different switching functions.

The further embodiments described below include a backlight 102, aninput polariser 106, a TFT substrate 108 and a pixel layer 110, as wellin some cases as an counter substrate 132, which are the same in theprior art system described above with reference to FIG. 7. For brevity adescription thereof is not repeated.

The detailed structure of one embodiment is shown in FIG. 14 in whichthe structure of the barrier and lenses are shown for both elementsoperating with parallel geometric axes, for illustrative convenience. Inpractice, the elements may be set at substantially 90 degrees to eachother, as described elsewhere in this application.

The display device 304 comprises the backlight 102 illuminating thedisplay panel comprising the input polariser 106, TFT substrate 108,pixel layer 110 and counter substrate 132. The pixel layer 110 is atransmissive spatial light modulator and the following optical elementsare arranged in series with, and on the output side of, the pixel layer110.

A polariser 308 is attached to the top of the counter substrate 132.

An additional substrate 310 has a switched liquid crystal cell whichacts as a polarisation control device and comprises ITO layers 312, 320,alignment layers 314, 318 and LC layer 316.

A passive birefringent lens is formed on the substrate 322, comprisingalignment layers (not shown), birefringent material 324 and isotropic,microstructured polymer 326 with a microstructured interface providing alens surface shaped as an array of lenses to direct light into aplurality of windows in the event of an index step being experienced. Inoperation, switching of the polarisation control device 312, 314, 316,318 controls the polarisation of the light passing through the lens 324,326 and hence the effect on the output light. The lens 324, 326 hassubstantially no effect on light of a first polarisation component butdirects light of a second polarisation component into a plurality ofviewing windows.

An active birefringent parallax barrier array is formed on substrates327 and 334 comprising a uniform ITO electrode 328, alignment layers(not shown), a liquid crystal layer 330 and a patterned electrode layer332. The patterned electrode layer 332 comprises slit regions 338 andbarrier regions 336. The barrier regions 336 may comprise firstelectrode regions while the slit regions 338 may comprise either noelectrodes whereby they are not addressable or second electrode regionswhereby they are addressable independently from the barrier regions 336.The patterned electrode layer 332 is driven to control the liquidcrystal layer 330 so that either light passes through both the slitregions 338 and barrier regions 336 whereby there is substantially nooptical effect or else light passes only through the slit regions 338whereby the output light is directed into a plurality of viewingwindows.

A final output polariser 340 is attached to the top of the stack andacts as an analyser polariser.

As will be apparent, the barrier array 328, 330, 332 is formed on theoutput side of the lens 324, 326 separately but without any polariser inbetween.

To simplify the explanation, it is assumed that there is no twistbetween the alignment on the plane substrate 322 and the geometricalaxis of the lens 326; in practical devices a twist may be present. Thelight output from the polariser 308 produces a linear outputpolarisation state with electric vector direction substantially parallelto the geometric axis of the lens 326.

In a first mode, no voltage is applied across the electrodes 312, 320 sothat the liquid crystal layer 316 rotates this polarisation componentthrough 90 degrees to be orthogonal to the lens geometric axis. For thispolarisation state, the refractive index of the polymer of the lens 326is matched to the ordinary refractive index of the liquid crystalmaterial 324 so that the microstructured surface therebetween is indexmatched and has substantially no optical effect on the directionaldistribution. The output polarisation is then incident on thebirefringent parallax barrier array layer 330. No voltage is applied tothe barrier electrode regions 336 so that the incident polarisation isparallel to the ordinary index of the liquid crystal material at thesurface adjacent layer 328. The output polarisation is rotated by 90degrees for the barrier regions 336 and slit regions 338 and outputthrough the polariser 340.

In this way, by operating in cooperation, neither the lens nor thebarrier are activated and the display operates without modification ofthe directional distribution, for example in the 2D mode of operation.

In the second mode of operation, just the birefringent lens array 324,326 is required to operate. In this mode, the LC layer 316 is activatedby a voltage applied across the electrodes 312, 320 and the polarisationoutput from the polariser 308 is thus unrotated. The light with thispolarisation is incident on the extraordinary axis of the birefringentmaterial 324 in the lens and thus the lens function is activated and thedirectional distribution is modified. The output polarisation state ispassed through the birefringent parallax barrier array 328, 330, 332unrotated by both barrier regions 336 and slit regions 338, by applyinga voltage to electrodes in both barrier regions 336 and slit regions 338in the case where both the barrier regions 336 and slit regions 338 areelectroded.

There may be gap between the barrier regions 336 and slit regions 338causing a relatively small area of the LC layer 316 to be unswitched orpartially switched. These areas may create residual absorption regionsacross the barrier. For a panel in use in the 3D mode, the lens array324, 326 may be arranged vertically. The barrier regions 336 and slitregions 338 may be arranged horizontally so that the resultant windowprofile will be vertical. However the residual absorption pattern willbe a small proportion of the total area so that the window intensityvariation as the display is tilted around a horizontal axis will be low.The display will appear to change intensity slightly as the display isrotated about a horizontal axis. Additionally, each eye will be atnominally the same height in the window, so there will be no noticeabledifference attributable to the birefringent parallax barrier array 328,330, 332 in the image between separate eyes.

Alternatively the slit regions 338 may have no electrode region so thatthe slit regions 338 appear to be black and the barrier regions 336white for this mode of operation. As the barrier regions 336(transmitting in this case)are much larger than the slit regions 338(absorbing in this case), the intensity variation of the windows willalso be relatively small. Thus the light which has seen the lens isoutput through the polariser 340, but the parallax barrier arrayfunction is substantially not activated.

In the third mode of operation, the liquid crystal layer 316 is notactivated so that the lens 324, 326 is index matched in thispolarisation and has substantially no optical function. However, in thebirefringent parallax barrier array 328, 330, 332, the slit regions 338are unactivated (by virtue for example of having no addressingelectrode) and thus rotate the input polarisation state while thebarrier regions 336 are activated. In this way, the polarisation statein the barrier regions 336 is unrotated and absorbed by the outputpolariser 340, while the polarisation state in the slit regions 338 isrotated and passed through the polariser 340.

Thus, it is possible to produce a display which is in a first mode a 2Ddisplay, in a second mode a lenticular screen 3D display for example forlandscape operation and a third mode a parallax barrier 3D mode forexample for portrait operation. For each mode of operation, the lens324, 326 and parallax barrier array 328, 330, 332 are placed between asingle pair of polarisers 308 and 340, and co-operate, based on thepolarisation state passed between the lens 324, 326 and parallax barrierarray 328, 330, 332. Advantageously it is not necessary to incorporatean additional polariser or multiple substrates between the lens andparallax barrier. This allows the apparatus to be fabricated with areduced number of substrates, reducing weight and cost. Advantageously,this also allows the separation of the barrier array 328, 330 from thepixel plane of the pixel layer 110 to be reduced, which reduces thenominal viewing distance of the display for a given window size.

Advantageously, each of the modes of the embodiment may enable the useof an output polariser 340 as the final element in the stack. Such apolariser reduces the visibility of frontal reflections from componentsin the display.

Advantageously, a polariser is not required to be attached, for exampleby means of lamination, between each of the parallax elements, that isthe lens 324, 326 and the parallax barrier array 328, 330, 332. Thismeans that the elements can be fabricated as an optical stack withoutthe need for additional surfaces on which to mount an intermediatepolariser. Thus, advantageously the number of substrates can be reduced,and the elements can be processed at elevated temperature prior toattachment of the polariser elements. This allows for further costreduction and integration of the structures. This also means thatmultiple elements could be made using a motherglass and divided, furtherreducing cost and complexity of manufacture, which would not generallybe possible if an intermediate polariser layer were required.

FIG. 15 shows the structure of an apparatus similar to that of FIG. 14except that the passive birefringent lens 324, 326 and polarisationcontrol device 312, 314, 316, 318, 320 is replaced by an active lenscomprising a birefringent lens 324, 326 across which an electric fieldcan be applied. In this case electrode layers for example as shown by323, 325 are applied on opposite sides of the birefringent lens 324, 326between the substrates 310 and 327. The operation of this embodiment isthe same as that of FIG. 14 except that the effect of the birefringentlens 324, 326 is controlled by the control signal across the electrodes323 and 325 rather than by control of the polarisation component oflight passing therethrough.

In the first mode, the birefringent lens 324, 326 is switched byapplying a voltage across the electrodes 323, 325 so that the outputpolarisation from the display sees the ordinary index of thebirefringent material 324 in the lens which is matched to the polymerindex of the polymer 326. The output polarisation is thus unrotated andsees the liquid crystal layer 330 to which no voltage is applied, sothat the output polarisation state is rotated to be outputted throughthe polariser 340. Thus the lens and barrier have no effect on thedirectional distribution of the display.

In the second mode of operation, no voltage is applied to thebirefringent lens 324, 326. The polarisation state from the polariser308 sees the extraordinary index of the birefringent material 324 and soa phase step is generated at the microstructured interface with thepolymer 326 and the lens function is produced. The output polarisationstate from the active birefringent lens 324, 326 may be in the samedirection as the output polarisation state for the first mode ofoperation. This output polarisation state from the birefringent lens324, 326 is again rotated by the layer 330 for both slit and barrierregions and output towards the observer so that no parallax barrierfunction is produced.

In the third mode of operation, the birefringent lens 324, 326 isactivated so that no phase step is seen in the birefringent lens 324,326, but the LC layer 330 has a voltage applied in the barrier regions336. In the slit regions 338 the polarisation in rotated and transmittedthrough the output polariser 340, whereas for the barrier regions 336,the polarisation is unrotated that the light passing through the barrierregions 336 is absorbed by the polariser 340.

The embodiment of FIG. 15 thus has the advantage that the structure hasfewer layers and thus may be less complicated to fabricate compared tothe passive lens configuration of FIG. 14. Additionally the slit regions338 are not required to have electrodes which reduces complexity.

As in the previous embodiment of FIG. 14, the parallax barrier array328, 330, 332 is required to operate in cooperation with thebirefringent lens 324, 326. This has the same advantages of reduced costand weight, together with reduced nominal viewing distance and reducedvisibility of frontal reflections, as described above.

In further embodiments, the parallax barrier and lens may use the sameliquid crystal layer so that they use common optical elements, as shownin FIG. 16. This embodiment is the same as that of FIG. 15 except thatthe ITO electrode 328, liquid crystal layer 330 and patterned electrodelayer 332 are omitted. Instead, the electrode 323 is patterned to havebarrier regions 336 and slit regions 338 which are independentlyaddressable. The liquid crystal layer 324 is arranged to have impart atwist, for example 90 degrees to polarised light passing through thecell. Also, a uniform switch cell 370 comprising for example a liquidcrystal layer with a 90 degree twist, and alignment layers (not shown)and ITO layers (not shown) is formed between substrates 327, 372.

By controlling the barrier regions 336 and slit regions 338 of theelectrode 323 together, the lens 324, 346 operates as a passivebirefringent lens as in the embodiment of FIG. 15. By controlling thebarrier regions 336 and 338 separately, the birefringent material 324(which is of course liquid crystal) may be operated to act as a parallaxbarrier.

In the first mode of operation, both barrier regions 336 and slitregions 338 are arranged to apply a voltage across the liquid crystallayer 324 so that the output polarisation from the polariser 308 isunrotated by the liquid crystal layer 324. The birefringent material 324in the lens is arranged so that there is an index match with the polymermaterial 326 at the lens surface and no phase function is produced. Inthe first mode, the cell 370 is arranged to rotate the outputpolarisation from the lens and transmit through the output polariser340, for example by applying no voltage to the cell.

In a second mode of operation, no voltage is applied across the liquidcrystal material 324 in either barrier regions 336 and slit regions 338,so that the output polarisation from the polariser 308 is incident onthe extraordinary index of the birefringent material 324. A voltage isapplied to the cell 370 and so the output from the lens is unrotated andpasses through the output polariser 340. Thus a lens function isproduced.

In a third mode of operation, a voltage is applied to the slit regions338, but not to the barrier regions 336. The light passing through theslit regions 338 thus sees no rotation of polarisation and is incidenton the ordinary index of the liquid crystal material 324 at the lenssurface such that the lens has no optical function. The cell 370 has novoltage applied so that the output is rotated and transmitted throughthe polariser 340. The light in the barrier regions 336 sees a rotation,and is incident on the extraordinary index of the liquid crystalmaterial 324 at the lens surface. However, this polarisation state isorthogonal to the output from the slit regions 338, and so is rotated bythe switch cell 370 and absorbed in the polariser 340. Thus the lightfrom the regions of the lens which see the phase function of the lens isabsorbed. Thus only the parallax barrier function is optimised.

Alternatively, patterned electrodes 323 may be applied under the polymer326 rather than within the liquid crystal cell.

Configurations in which the parallax barrier and lenticular screen arein nominally the same plane have advantages for landscape and portraitoperation in systems using RGB strip pixel patterns. In particular, thesize of the optical spot at the pixel plane may be different forlandscape and portrait operation. In landscape operation for a panel asshown for example in FIG. 11 d, the lens may be designed to produce atightly focussed spot, and thus high window quality. The barrier may bedesigned to produce a wide, but advantageously achromatic, spot whichcovers a red, green and blue colour sub-pixel. Thus, an autostereoscopicimage may be produced, each orientation of which is optimised.

The apparatus of FIG. 17 is configured in a similar manner to thestructure of FIG. 16, but using a solid liquid crystal lens component374 and liquid crystal layer 376 in place of the birefringent material324. The electrode layer 325 may be formed on the substrate 327 or maybe at the plane surface of the solid liquid crystal lens component 374.A thin substrate (not shown) may alternatively be placed between thelayers 376, 374.

In the first mode of operation, the barrier and slit regions 336, 338are arranged with no voltage applied so that the polarisation state fromthe polariser 323 is rotated through the liquid crystal layer 376 and isincident on the ordinary index of the solid liquid crystal lenscomponent 374 which is index matched to the polymer 326. The output isthen rotated by the cell 370 with no voltage applied and transmittedthrough the output polariser 340.

In the second mode of operation, both the barrier and slit regions 336,338 have a voltage applied so that the polarisation state in the liquidcrystal layer 376 is unrotated and incident on the extraordinary indexof the solid liquid crystal lens component 374. The lens thus has a lensfunction. A voltage is applied to the cell 370 so that the output istransmitted through the output polariser 340.

In the third mode of operation, a voltage is applied in the barrierregions 336, so that in the slit regions 338, the polarisation state isrotated and transmitted through the liquid crystal layer 370 with novoltage applied. In the barrier regions 336, the polarisation state isunrotated and so sees the extraordinary index of the lens 374, 326 and alens function is produced. However, this polarisation state is rotatedby the layer 370 and absorbed by the polariser 340. Thus, a parallaxbarrier element is produced.

The embodiments of FIGS. 16 and 17 may be simplified by removing theoutput polarisation switching cell 370. Such a display apparatus may beconfigured to have a first mode in which the directional distribution ofthe output light is not substantially modified and a second mode inwhich both parallax barrier and lens produce a plurality of first andsecond viewing windows, respectively.

In further embodiments, the parallax barrier element may be placedbetween the lens and panel. Typical mobile display panels comprise red,green and blue vertical stripes of pixels, when viewed in the portraitmode. Thus the pixel width in portrait mode is approximately one thirdof the pixel width in the landscape mode.

The barrier may preferably be used to image the pixels in the portraitmode, while the lens may preferably be used to image the pixels in thelandscape mode. Thus the portrait mode parallax element should be closerto the pixels than the landscape mode device in order that the viewingdistance of the display in each mode is similar.

Additionally, in a landscape mode parallax barrier, the barrier regionsbetween the slits of the barrier may be more visible to the human eyecompared to the barrier region between the slits in the portrait mode.Lenses do not suffer from the same barrier region visibility problem,because there is a continuous intensity across the lens aperture.Therefore, it may be advantageous to set the parallax barrier to imagethe pixels in the portrait mode, and thus closer to the display pixelplane than the lenses. An apparatus which is an example of this is shownin FIG. 18, this being the same as the apparatus of FIG. 15 except thatthe substrate 327, the electrode 328, alignment layers (not shown), theliquid crystal layer 330 and the patterned electrode layer 332 arearranged on the substrate 310, that is between the lens 324, 326 and thepixel layer 110. The operation of the apparatus of FIG. 18 is identicalto that of the apparatus of FIG. 15.

In the apparatus shown in FIG. 19, the birefringent parallax barrier328, 330, 332 is positioned between the lens 324, 326 and the pixellayer 110 as in the apparatus of FIG. 18. An additional uniformswitching liquid crystal layer 350 with additional switching electrodes352, 354 is positioned in series between the birefringent lens 324, 326and the parallax barrier 328, 330, 332. The output polarisation from thepolariser 308 may be at an angle to the geometric lens axis, for example45 degrees. In this way, 50% of the incident light will be resolved onto the extraordinary axis of the lens material 324, and 50% on to theordinary axis of the lens material 324.

In operation in a first mode, the parallax barrier layer 330 isunswitched so that the output state is rotated to −45 degrees. This isincident on to the passive birefringent lens 324, 326 and so the lens324, 326 has an optical function for 50% of the light. The liquidcrystal layer 350 is unswitched and rotates both resolved polarisationcomponents. The final polariser transmits half of the resultantillumination, corresponding to the lens 324, 326 having no opticalfunction.

In the second mode of operation, the layer 350 is switched so that nopolarisation rotation takes place and the optical function of the lens324,326 is transmitted.

In the third mode of operation, the parallax barrier 328, 330, 332 isswitched so that the barrier regions 336 rotate the incidentpolarisation state by 90 degrees while the slit regions 338 do notrotate the polarisation. Both states fall on to the lens 324, 326, andthe final shutter is unswitched so that the lens 324, 326 has no opticalfunction for the light that had passed through the slit regions 338 ofthe parallax barrier 328, 330, 332 and is transmitted through the finaloutput polariser 340. The light that was transmitted through the barrierregions 336 is incident on the extraordinary axis of the lens 324, 326and thus has a lens function. However, after passing through the finalswitch layer 350, this light is extinguished by the output polariser340. Thus, only the barrier function is transmitted through the outputpolariser 340.

In terms of operation, the apparatus of FIG. 19 is very similar to theapparatus of FIG. 17, but the embodiment of FIG. 17 has the advantage ofbeing thinner in that there is no substrate corresponding to thesubstrate 327 between the liquid crystal layer 376 and the lenscomponent 374.

In an alternative embodiment, the switch layer 350 can be positionedbetween the parallax barrier 328, 330, 332 and the lens 324, 326.

In an alternative embodiment, the parallax barrier 328, 330, 332 can beconfigured as in FIG. 19 such that the barrier regions 336 and slitregions 338 are both comprised of separately addressable electroderegions. In the first mode, both barrier layer 330 and switch layer 350are deactivated, and the polarisation output direction from the panel isparallel to the geometric lens axis. In the second mode, the switchlayer 350 and both the barrier 336 and slit 338 electrode regions areactivated. In the third mode, the barrier 336 electrodes are activated,and the slit 338 electrode and switch 350 electrodes are deactivated. Inthis way the display can be configured advantageously to have fullbrightness.

FIG. 20 shows the case of a display apparatus with a switchable parallaxbarrier 328, 330, 332 on the input side of the pixel layer 110 and apassive birefringent lens 324, 326 on the output side of the pixel layer110. In particular the apparatus of FIG. 20 is the same as that of FIG.14 except as follows.

The display panel comprises input polariser 106, pixel layer 110 betweensubstrates 108 and 132, and output polariser 308. The birefringentparallax barrier layer comprising elements 310, 328, 330, 332, 334 ispositioned on the input side of input polariser 106. The electrode 332has barrier regions 336 and slit regions 338 having a pitch set to beslightly greater than the pitch of the barrier regions 336 and slitregions 338 in the electrode 332 of the equivalent parallax barrier 328,330, 332 arranged on the output side of the pixel layer 110 in FIG. 14,in order to compensate for the viewing geometry of the display, as knownfor rear parallax barrier elements in general. An input polariser 307 isdisposed on the input side of substrate 310.

A uniform switching liquid crystal layer 362 with additional switchingelectrodes 352, 354 is positioned between the display panel 323, 108,110, 132, 106 and the birefringent lens 324, 326.

In operation in a first mode, the light from the backlight 102 ispolarised by the input polariser 307 and is incident on the parallaxbarrier layer 330 which is unswitched in both barrier regions 336 andslit regions 338; so a uniform polarisation is incident on the displaypanel input polariser 106. The switch layer 350 is arranged to rotatelight from the display panel output polariser 106 so that the lensfunction of the birefringent lens 324, 326 is not seen and a standard 2Ddisplay mode results.

In the second mode of operation, the layer 330 is unswitched and thelayer 350 is switched so that no polarisation rotation takes place andthe polarisation state from the output polariser 308 thus sees the lensfunction of the birefringent lens 324, 326 and light output from theapparatus is directed into a plurality of viewing windows.

In the third mode of operation, the birefringent parallax barrierelectrode 332 is switched so that the incident polarisation state isrotated by 90 degrees in the barrier regions 336 while the incidentpolarisation state is not rotated in the slit regions 360. The switchcell 362 is arranged so that the lens function of the birefringent lens324, 326 is not seen but the parallax barrier 328, 330, 356 directslight into a plurality of viewing windows.

Thus in this embodiment, the birefringent lens 324, 326 is passive andswitching is performed by control in the switching liquid crystal layer362 of the polarisation of the light passing through the birefringentlens 324, 326.

As an alternative, the birefringent lens 324, 326 could be replaced byan active birefringent lens with lens electrodes as in the embodiment ofFIG. 15. An example of this is the apparatus shown in FIG. 31 which isthe same as the apparatus of FIG. 20 except that the passivebirefringent lens 324, 326 and polarisation control device 352, 362, 354are replaced by an active birefringent lens 324, 326 having electrodes323 and 325.

In one mode of operation, both the lens 324, 326 and barrier 328, 330,332 are arranged to have no effect on the incident light. In anothermode, the parallax barrier 328, 330, 332 is operated, while the lensfunction of the lens 324, 326 is not enabled. In another mode, theparallax barrier 328, 330, 332 has no effect while the lens 324, 326 isoperated.

Such an apparatus advantageously has a short separation between thepixel plane formed by the pixel layer 110 and both the lens 324, 326 andthe parallax barrier 328, 330, 332, thus reducing viewing distance. Theapparatus further has high efficiency in two of the three modes.

A further apparatus is shown in FIG. 26 which is the same as that ofFIG. 14, except as follows. A birefringent lens is configured using asolid liquid crystal material 424 which has been formed on the surfaceof the polymer 326. Such a lens may be formed by means of filling a cellwith appropriate alignment layers with the solid liquid crystal material424 as a monomer while in the nematic phase, and subsequently curing thematerial. The plane substrate (not shown) is then removed to provide theplane surface 426 of the solid liquid crystal material 424. Such aconfiguration advantageously allows the removal of an additionalsubstrate, and thus allows for a shorter viewing distance.

Instead of the polarisation control device formed by elements 312, 320314, 316, 318, the apparatus has a polarisation control device formed bya liquid crystal layer 428 disposed between the solid liquid crystalmaterial 424 and substrate 430. Alignment layers and ITO electrodes (notshown) are used to align and address the layer 428. Operation of theapparatus is the same as the apparatus shown in FIG. 14.

FIG. 28 shows a further apparatus in which a passive birefringent lensdisplay cooperates with a parallax barrier. The apparatus of FIG. 28 issimilar to that of FIG. 26, except as follows. The apparatus uses asolid birefringent lens component 424 arranged on the output surface ofthe display substrate 132. Advantageously, this allows a short viewingdistance with high resolution image pixels.

A polarisation rotation device 440 acting as a polarisation controldevice is arranged on the output side of the lens 424, 326 on substrate438. The polarisation rotation device 440 includes ITO electrodes andalignment layers (not shown). A further ITO substrate 442 with alignmentlayers 442 is attached. The parallax barrier 328, 330, 332 is attachedto the top surface of an additional polariser 444.

In the first mode of operation, the polarisation rotation device 440 isarranged to transmit the index matched polarisation through thepolariser 444. The barrier 328, 330, 332 is arranged to rotate theoutput polarisation for slit regions 338 and barrier regions 336.

In the second mode, the light which experiences the phase function ofthe lens 424, 326 is outputted through the polariser 444, and thebarrier 328, 330, 332 operates in the same manner as for the first mode.

In the third mode of operation, the lens 424, 326 is arranged to beindex matched as in the first mode, and the barrier 328, 330, 332 isarranged to rotate the output polarisation from polariser 444 in theslit regions 338 and not to rotate the polarisation of the light fromthe barrier regions 336. Thus, the light from the barrier regions 336 isabsorbed in the polariser 340 and the barrier output is observed.

FIG. 29 shows a further apparatus which is the same as that of FIG. 28except that an additional polariser 446 is incorporated between thepanel substrate 132 and the lens 424, 326. The optical axis of the lens424, 326 is arranged to be at 45 degrees to the output polarisation ofthe display. Operation is similar to that of FIG. 28. Advantageously,such a display works well with high resolution panels.

In the apparatuses described above, the parallax barrier may comprise apatterned half wave retarder element in combination with a polarisationswitch. Such an element has the advantage that the separation of thepatterned half wave retarder from the pixel plane of the display may beminimised.

In the active lens embodiments of the present invention, addressingelectrodes such as ITO or using a conductive polymer may be formed onthe microstructured polymer surface, under the polymer surface or withinthe polymer material.

In each of the embodiments of the invention, further waveplates may berequired to be inserted so as to rotate the output polarisation of thepanel in the appropriate orientation with respect to the birefringentparallax optical components.

Various of the parallax barriers of the invention described so far havea slit region which is un-activated and a barrier region which can beactivated. It may be possible to replace the barrier regions with aswitchable polarisation twisting layer and the slit regions with anon-rotating layer. The non-rotating layer may be a birefringentmaterial which causes no rotation of polarisation, or may be anon-birefringent material. It may be necessary to adjust thepolarisation transmission directions accordingly.

It may be desirable to use a parallax barrier in two modes of operationin two modes, which may simplify construction. FIG. 21 shows anotherdisplay apparatus in which two parallax barriers are configuredadvantageously between a single pair of polarisers 308, 340 to havethree modes of operation. The display apparatus is the same as that ofFIG. 21 except that the birefringent lens 324, 326 and the polarisationcontrol device 312, 314, 316, 318 is replaced by a second parallaxbarrier comprising electrodes 342, 344 disposed on opposite sides of aliquid crystal layer 346. Thus the second parallax barrier 342, 344, 346is placed between the first barrier 328, 330, 332 and the pixel layer110.

Both the first barrier 328, 330, 332 and the second parallax barrier342, 344, 346 have patterned electrodes with switchable barrier regions336 and non-switchable slit regions 338.

In the first mode of operation slit regions 338 and barrier regions 336of both the first barrier 328, 330, 332 and the second parallax barrier342, 344, 346 are set to rotate the polarisation state through 90degrees so that a uniform illumination is passed through the outputpolariser 340.

In the second mode of operation the electrode 344 is set so that thepolarisation state in the liquid crystal layer 346 is rotated in thebarrier regions 336 and unrotated in the slit regions 336. No voltage isapplied to the liquid crystal layer 330 so that the output polarisationstate corresponding to the barrier layer 346 is absorbed or transmitteddepending on whether the light passes through the slit regions 338 orthe barrier regions 336 respectively. Thus the barrier regions 336 ofthe first barrier 328, 330, 332 are resolved and the first barrier 328,330, 332 directs light into a plurality of viewing windows.

Similarly in a third mode of operation, for the second parallax barrier342, 344, 346, the layer 330 is addressed while the layer 346 isuniform, so that the second parallax barrier 342, 344, 346 directs lightinto a plurality of viewing windows.

Such a configuration is particularly advantageous, as the sizes ofpixels tends to be different in landscape and portrait configurations.Thus the first barrier 328, 330, 332 and the second parallax barrier342, 344, 346 for the two configurations can be set at the correspondingseparations so that the final viewing distance is nominally the same forboth portrait and landscape modes. Such an apparatus makes efficient useof the light in the 2D mode, but suffers from losses in the 3D mode.Such an apparatus does not require the use of separate polarisers orsubstrates between each element and thus reduces complexity and costwhile optimising viewing distance of the display in each mode ofoperation.

Alternatively, the nominal viewing distances may be set to be differentto optimise the usability of the display for each panel orientation.

In various of the configurations of the display apparatuses there is afurther mode of operation which give both vertical and horizontalparallax with respect to the image by allowing both apparatuses tooperate at the same time. However, for a parallax barrier display, thiswould produce a low optical efficiency.

As shown in FIG. 30, the colour sub-pixel columns 452, 454, 456 may bearranged in the portrait mode for example so that four columns of pixelapertures are placed in alignment with each optical element of theparallax array 458. Each element of the parallax array 458 may beconfigured so as to provide an eye spot 460 which is substantially thesame as the pitch of the pixel columns at the pixel plane. The windowsize may be set to be substantially half of the nominal interocularseparation for example by adjusting the pitch of the parallax elements.Such a configuration advantageously provides a shorter viewing distancefor a fixed substrate glass thickness. Further, such an element servesto reduce the visibility of the image of the black mask in the windowplane. Advantageously, the parallax element in this orientation may be aparallax barrier, such that the chromatic aberrations of the display andviewing angle are optimised in this mode of operation.

Such a configuration may for example use a lens 462 with two rows 450,451 of pixels under each lens in the landscape orientation in which theeye spot 464 is small so as to optimise the viewing freedom of thedisplay, and a parallax barrier in the portrait orientation with fourcolumns of pixels aligned with each slit of the parallax barrier. To setthe viewing distance to be the same in each orientation, the opticalelements 458, 462 may be arranged at different respective distances fromthe pixel plane, in this case, the lenses being 50% further away fromthe pixel plane than the barriers. Alternatively, the colour sub-pixelsrepeat pitch may be changed from 1:3 to 1:2, so that the width of 4colour sub-pixels may be the same as the width of 2 pixels. Such aconfiguration advantageously allows both parallax elements to benominally in the same plane while providing the same viewing distance,thus reducing cost and complexity while optimising image quality in bothmodes of operation.

In all of the above embodiments, the images on the panel may be adjustedto suit the mode of operation of the panel. For example, in thelandscape mode of operation, the pixel columns on the panel are arrangedto display alternate columns of left and right eye data. In the portraitmode of operation, the pixel rows are arranged to display alternate rowsof left and right eye data.

In a further aspect of the present invention, a directionalautostereoscopic display apparatus is configured to have a firstnon-directional mode and a second directional mode with combinedlandscape and portrait operation, in which the landscape and portraitoptical elements are formed with a common birefringent material. Theoptical elements may be lenses. The lenses may be cylindrical lenses.

Such a display apparatus is shown in FIG. 22 and is the same as theapparatus shown in FIG. 14 except that the elements disposed on theadditional substrate 310 are replaced by the following elements.

Disposed on the additional substrate 310 is a birefringent lens arraycomprising a pair of lens structures 380, 382 each formed as a layer ofisotropic, polymer material and a common birefringent material 384disposed between the lens structures 380, 382. The surfaces of lensstructures 380, 382 interfacing with the birefringent material 384 areeach shaped as lens surfaces providing an array of cylindrical lenses.The lens structure 382 is optimised for landscape operation and the lensstructure 384 is optimised for portrait operation. Thus the cylindricallenses of both the lens structures 382 and 384 extend substantiallyorthogonally to one another (although for clarity they are shown asbeing parallel in FIG. 22). The cylindrical lenses of both the lensstructures 382 and 384 are shaped to direct light into a plurality ofviewing windows. The viewing windows may be arranged to provide anautosterescopic 3D effect.

Both lens structures 380 and 382 have a refractive index equal to theordinary refractive index of the birefringent material 384 (or in analternative embodiment the extraordinary refractive index of thebirefringent material 384).

Electrodes 323 and 325 are disposed on opposite sides of the lensstructure 380 and lens structure 382 so that the birefringent material384 may be switched by applying an electric field across the electrodes323 and 325. Thus the birefringent lens array 380, 382, 384 is active.

A final output polariser 340 is attached to the top of the stack andacts as an analyser polariser.

In a first mode of operation, the birefringent material 384 is switchedso that the light passing therethrough of the polarisation componentoutput by the output polariser 340 experiences the ordinary refractiveindex of the birefringent material 384 (or in the alternative embodimentthe extraordinary refractive index of the birefringent material 384).This light experiences no index step at the lens surfaces of the lensstructures 382 and 384 so in this mode the light output from the displayapparatus experiences substantially no directional effect from thebirefringent lens array 380, 382, 384.

In a second mode of operation, the birefringent material 384 is switchedso that the light passing therethrough of the polarisation componentoutput by the output polariser 340 experiences the extraordinaryrefractive index of the birefringent material 384 (or in the alternativeembodiment the ordinary refractive index of the birefringent material384). This light experiences an index step at the lens surfaces of thelens structures 382 and 384 so in this mode the light output from thedisplay apparatus experiences a directional effect from both theopposing lens surfaces of the birefringent lens array 380, 382, 384.

Advantageously, at least one of the lens structures 380 and 382 mayitself incorporate a conductive element, or be a conductive polymer, inwhich case the electric field is not dropped across the polymer layer.

In the apparatus shown in FIG. 23, the birefringent lens 380, 382, 384is passive instead of active. This apparatus is the same as that of FIG.22 except that the electrodes 323 and 325 are omitted and instead apolarisation switch is formed by a liquid crystal layer 330 disposedbetween electrodes 328 and 332 and is used to control the polarisationstate that passes through the liquid crystal layer 330 and to the userthrough the analyser polariser 340.

In a first mode of operation, the polarisation switch 328, 330, 332 isswitched so that the light output by the output polariser 340 is thepolarisation component which experiences the ordinary refractive indexof the birefringent material 384 (or in the alternative embodiment theextraordinary refractive index of the birefringent material 384). Thislight experiences no index step at the lens surfaces of the lensstructures 382 and 384 so in this mode the light output from the displayapparatus experiences substantially no directional effect from thebirefringent lens array 380, 382, 384.

In a second mode of operation, the polarisation switch 328, 330, 332 isswitched so that the light output by the output polariser 340 is thepolarisation component which experiences the extraordinary refractiveindex of the birefringent material 384 (or in the alternative embodimentthe ordinary refractive index of the birefringent material 384). Thislight experiences an index step at the lens surfaces of the lensstructures 382 and 384 so in this mode the light output from the displayapparatus experiences a directional effect from both the opposing lenssurfaces of the birefringent lens array 380, 382, 384.

FIG. 27 shows a further apparatus which is the same as that of FIG. 23except modified so that solid liquid crystal lenses 432, 434 are formedon the respective substrates 310 and 327, and attached by anintermediate polymer layer 436. Thus, the optical function of thedevices is preserved, but the fabrication process is modified. Such astructure may advantageously reduce the assembly cost of the apparatus.

In each of the apparatuses of FIGS. 22, 23 and 27, the lenses are shownfor purposes of illustration as being aligned in the same axis, but infact their geometric lens axes are rotated by 90 degrees with respect toeach other. Each lens may be rubbed advantageously parallel to the lensaxis, so that there is a 90 degree twist in the material 384 between thetwo lenses. Thus, the polarisation component from the output polariser308 which sees the lens surface of the lens structure 382 also sees thelens surface of the other lens structure 384, and the polarisationcomponent from the output polariser 308 that is index matched seessubstantially no lens function.

The passive lens configuration of FIG. 23 has the particular advantage,that the performance of the birefringent lens 380, 382, 384 is notdetermined by the thickness of the lens structures 380, 382. The voltagein an active lens configuration of FIG. 22 is further increased, becausein certain regions, the birefringent lens 380, 382, 384 will have up totwice the thickness of a single lens, and so the relaxation time of thebirefringent lens 380, 382, 384 is significantly increased. This meansthat the lens will switch only slowly between 2D and 3D modes inparticular. Also, a very high voltage is required to provide operationin the display of FIG. 22, and the performance of the passive lensconfiguration will be improved with respect to an active lensconfiguration.

In each cases, the radius of the cylindrical lenses may advantageouslybe different so that in the landscape mode for example, a tightlyfocussed eye spot is used whereas in the portrait mode, a wide spot maybe used which covers three columns of colour sub-pixels.

In a further aspect of the present invention, alignment features areincorporated into the optical structures so as to provide preciserelative alignment to the two features, without the need to provide highprecision measurement for each optical structure on a panel by panelbasis.

Such a configuration requires high precision alignment between the twolens structures, in addition to alignment in vertical and horizontaldirections when the combined structure is aligned on the panel. This canbe achieved by incorporating registration features at the edge of eachlens structure 380 and 382 as shown schematically in FIG. 24. Alignmentfeatures 410, 412 may be incorporated in to the polymer structures 380,382, such that the lenses mate at the correct angle with respect to eachother. This is shown further in plan view in FIG. 25 for the firstsubstrate 327 with lens geometric optical axis 416 and alignmentfeatures 414 which mate to alignment features 420 on the secondsubstrate 310 with lens geometric optical axis 418. The alignmentfeatures may run vertically on one side and horizontally on the other,for example features 420 may be vertically extending, while features 422may be horizontally extending on both substrates.

During assembly of the optical component, the two components are broughtclose to each other and mated using the alignment features. Thus, a highaccuracy alignment tool is not required to set the relative anglebetween the two surfaces.

The features may advantageously be repetitive features with pitches thesame as the lens pitch in the particular direction. Thus for example thepitch of features 422,424 in FIG. 24 is the same as the lens pitch oflenses 380. Alternatively, the features may have be two dimensionalstructures to constrain the relative position of the two components inboth first and second directions. The alignment features may beincorporated in the lens master, and thus may be replicated at low cost.Such structures advantageously remove the need for a high tolerancealignment step between the two lenses, and thus reduce the cost ofmanufacture of the system.

When the second substrate is a parallax barrier component and the firstsubstrate is a lenticular screen, it may be possible to use alignmentfiducials on each substrate to complete the alignment between the twolayers. The lens may incorporate optical imaging function whichcooperates with fiducials on the parallax barrier to produce a signalfor automatic alignment of the two components.

Thus, in a further aspect of the invention, alignment features may beconfigured with the same pitch as the optical structures, first featuresproviding alignment in a first direction and second features providingalignment in a second direction, in which the pitch of the features infirst and second directions is the same as the pitch of the opticalstructures in the first and second direction respectively.

The alignment elements may further be positioned on a first parallaxbarrier surface and a second lens surface.

In the above-described embodiments, the liquid crystal material used inthe various parallax elements may be a liquid crystal or a liquidcrystal gel, for example. A liquid crystal gel may comprise a network ofpolymer material and a liquid crystal material. The polymer material maybe a liquid crystal polymer material. In the case of a passivebirefringent lens, the liquid crystal material may be polymerised liquidcrystal material.

In each of the above-described embodiments, the addressing of theelements may be modified so that over some areas, the display apparatusoperates in the first mode and over areas the display apparatus operatesin the second or third modes.

In the above-described embodiments incorporating an active parallaxbarrier comprising a switchable liquid crystal layer, the activeparallax barrier may be replaced by a passive parallax barrier whichcomprises a patterned array of half-wave retarders and a switchablepolarisation control device. Such a configuration has the advantage thatthe viewing distance of the display apparatus may be reduced as theretarders may be placed close the pixel plane of the spatial lightmodulator. The slit regions of such an element may not be independentlyaddressable.

1. A display apparatus comprising: a spatial light modulator; and abirefringent lens array arranged in series with the spatial lightmodulator and comprising a layer of birefringent material between twoopposing lens surfaces, the lens surfaces each shaped as an array ofcylindrical lenses extending substantially orthogonally to each other,the display apparatus being switchable between a first mode in which thebirefringent lens array has substantially no directional effect on lightoutput from the display apparatus and a second mode in which thedirectional distribution of the light output from the display apparatusis modified by both of the opposing lens surfaces.
 2. A displayapparatus according to claim 1, wherein the birefringent lens array isan active birefringent lens array comprising electrodes for applying anelectric field across the layer of birefringent material, the displayapparatus being switchable between the first and second modes byswitching of the voltage applied across said electrodes.
 3. A displayapparatus according to claim 1, wherein the birefringent lens array is apassive birefringent lens array and the display apparatus furthercomprises a switchable polarisation control device arranged in serieswith the birefringent lens array which is switchable to pass light ofeither a first polarisation component or a second polarisationcomponent, the birefringent lens array having substantially nodirectional effect on light of the first polarisation component andmodifying the directional distribution of light of the secondpolarisation component, the display apparatus being switchable betweenthe first and second modes by switching of the switchable polarisationcontrol device.
 4. A display apparatus according to claim 1, wherein thetwo opposing lens surfaces are formed as the surfaces of two respectivelayers of material, which layers of material are provided outside thelens surfaces with alignment features which engage each other to alignthe lens surfaces relative to each other.
 5. A display apparatusaccording to claim 1, wherein the display apparatus is anautostereoscopic display apparatus and the cylindrical lenses are fordirecting light from the spatial light modulator into a plurality ofviewing windows.